| XXX | (296) | XXX |
296 A N A T portion, and form a *ci«d of cutaneous tube in the other portion. The fitin which covers both fides of the cartilage contains a great number of finall glands, which continually difcharge an oily whitifh humour, collected chiefly near the adhefions of the ear to the head, and under the fold of the helix ; and thefe glands are of the febaceous kind. The fkin which lines the meatus auditorius contains another kind of glands, of a yellowifh colour, and which may be plainly leen on the convex fide of the cutaneous tube already mentioned. Thefe glands are difpofed in fech a manner as to leave reticular {'paces between them, and they penetrate a little way into the fubftance of the fkin. They are called glandule ceruminofe, becaufe they difcharge that matter which is named cerumen, or the wax of the ear. The inner furface of the cutaneous tube is full of fine hairs, between which lie the orifices of the ceruminous glands. The firfl place in which we meet with thefe glands is on that part of the convex fide of the cutaneous tube which fupplies the breaks of the cartilaginous meatus. All the bony parts of the organ of hearing, or bones of the internal ear, being contained in the inferior portions of the OfTa teroporum; it will be very proper to recoiled! what has been already faid about thefe, in Part I. All the bony organ of hearing may be divided into four general parts : i. The external meatus auditorius; 2. The tympanum or barrel of the ear; 3. The labyrinth; 4.. The internal meatus auditorius. It may likewife be divided into immoveable or containing parts, which take in all the four already mentioned ; and moveable or contained parts, which are four little bones lodged in the tympanum, called incus, malleus, Jlapes, and os orbiculare or Jenticulare. The external auditory pafTage begins by the external auditory hole, the edge of which is rough and prominent; but backwards towards the maftoid apophyfis it appears very much floped. The paffage itfelf is about half an inch in length, running obliquely from behind forward, in a curve direction, and fometimes winding a little in the middle, like a ferew. Its cavity is almoft oval, wider at the entry than at the middle, after which it widens again by degrees. It terminates inwardly by an even circular edge lying in aplane very much inclined,' the upper part of it being turned outward, and the lower part inward; fo that the whole canal is longer on the lower fide than on the upper. The concave fide of the circular edge is grooved quite round. In children this bony canal is wanting, as well as the maftoid apophyfis; and the inner circular edge is a difrinct ring, which in an advanced age unites intirely, and becomes one piece with the reft. It is termed the bony circle in infants, and indeed it is very eafily feparated from all the other parts. It would feem therefore, that the whole bony canal in adults is only a prolongation of the bony circle in children ; becaufe even in a more advanced age, the whole canal may, without much difficulty, be taken out. The circular groove lies between the maftoid apophyfis and the articular fiflure ©r crack.
O M. Y. Part VI. The tympanum or barrel of the ear is a cavity irre-1 gv.larly fgmi-fphericaJ, the bottom of it being turned in ward, and the mouth joined to the circular groove already mentioned. Both eminences and cavities ate obfervable in it. The remarkable eminences are three in number; a large tuberofity lying in the very bottom of the barrel, a little toward the back part; and a fmall irregular pyramid fituated above the tuberofity, and a little more backward ; the apex of it is perforated by a fmall hole, and on one fide of the bafis two finall bony filaments are often found in a parallel fituation. In the third eminence is a cavity fhaped like the mouth of a fpoon, fituated at the upper and a little towards the anterior part of the bottom of the tympanum. The principal cavities in the tympanum are, the opening of the mafloid cells or finuofities; the opening .of the Euftachian tube; the bony half-canal ; the feneflra ovalis and rotunda; and to thefe may be added the fmall hole in the pyramid. The opening-in the maftoid cells is at the pofterior and upper part of the edge of the barrel. The cells themfelves which end there are dug in the fubftance of the maftoid procefs, being very irregular and full of windings and turnings. The opening of the Euftacljian tube is at the anterior and a little toward the upper part of the edge of the barrel. This tube runs from the tympanum, towards the pofterior openings of the nafal foffie, and arch of the palate. The bony portion thereof is dug in the apophyfis petrofa, along the duft of the carotid apophyfis; and when it leaves that, it is lengthened out by the fpinal apophyfis cf the os fphenoides. The bony half-canal, of which the cavity refembling the mouth of a fpoon is the extremity, lies immediately above the Euftachian tube, towards the upper fide of the apophyfis petrofa, or rather in the very fubftance of that upper fide. The feneftra ovalis is a bole of communication between the tympanum and labyrinth. It lies immediately above the tuberofity, the upper fide of it being a little rounded, the lower a little flatted ; and one extremity being turned forward, the other backward. The feneftra rotunda is fomething lefs than the ovalis, and fituated in the lower, and a little towards the pofterior part of the large tuberofity ; the opening of it, which is the orifice of a particular dufi in the labyrinth, lying obliquely backward and outward. The hole in the apex of the pyramid is the orifice of a cavity, which may be named the firms of this pyramid. The tympanum contains feveral little bones called the hones of the ear. They are generally four in number, denominated from fomething to which they are thought to bear a refemblance, viz. incus, malleus, ftapes, and os orbiculare or lenticuiare The incus, or anvil, refembles, in fome meafure, one of the anterior grinders with its roots at a great diftance from each other; at leaft it comes nearer to this than to the fhape of the anvil. It may be divided into a body and branches. The body is a large fubftance, the branches
